(1) Field of the Invention
The present invention generally relates to a catalyst heating apparatus, and more particularly to an apparatus for supplying power to an electrically heated catalyst converter mounted in an exhaust passage of an internal combustion engine for catalytic conversion of exhaust gases from the engine.
(2) Description of the Related Art
Conventionally, in an automotive vehicle, a catalyst converter is mounted in an exhaust passage of an internal combustion engine for catalytic conversion of exhaust gases from the engine. Catalytic conversion signifies catalytic activity by a catalyst contained in the catalyst converter for accelerating oxidization of carbon monoxide and hydrocarbon pollutants in the exhaust gases and/or reduction of oxygen nitride pollutants in the exhaust gases. However, the catalytic activity or the catalytic conversion efficiency of a catalyst is relatively low when the temperature of the catalyst is still low; before a certain temperature level is reached. Once the engine starts operating, the temperature of the catalyst gradually increases due to the heat of exhaust gases passing into the exhaust passage, but if the engine is not warmed up, during a cold start, for example, and the temperature of exhaust gases is low, the temperature of the catalyst in the converter does not rise quickly to a required temperature level. Thus, there is a problem in that the engine in such a condition exhibits a poor fuel combustion efficiency, and the catalytic conversion efficiency of the catalyst is low.
In the prior art, there is a disclosure of a catalyst converter. For example, Japanese Laid-Open Utility Model Application No. 49-36324 discloses a conventional catalyst converter device for an internal combustion engine. This catalyst converter device includes a heater or a heating element provided within a catalyst converter on its upstream side in an exhaust passage of the engine. The heater, connected to a circuit of a starting motor of the engine, is energized when engine operation is started by the starting motor, and serves to preheat unburned components in exhaust gases, for catalytic conversion of the exhaust gases before the catalyst converter is filled with exhaust gases from the engine.
However, the above mentioned catalyst converter uses a battery as the power source for supplying electric power to the heater of the catalyst converter. A resistance of the heater is constant with respect to temperature changes of the heater, and the electric power supplied by the battery to the heater when the engine starts operating, especially during a cold start, cannot be adjusted in the case of the above catalyst converter device. Thus, there is a problem, in the case of the conventional device, in that it is difficult to attain a rapid increase of the temperature of the heater during a cold start of the engine, and in that it is difficult to shorten a time for the catalyst to heat up for efficient catalytic conversion of exhaust gases.